This is a note to let you know that I've just added the patch titled

nohz: Prevent a timer interrupt storm in tick_nohz_stop_sched_tick()

to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: nohz-prevent-a-timer-interrupt-storm-in-tick_nohz_stop_sched_tick.patch and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 5d62c183f9e9df1deeea0906d099a94e8a43047a Mon Sep 17 00:00:00 2001

From: Thomas Gleixner tglx@linutronix.de Date: Fri, 22 Dec 2017 15:51:13 +0100 Subject: nohz: Prevent a timer interrupt storm in tick_nohz_stop_sched_tick()

From: Thomas Gleixner tglx@linutronix.de

commit 5d62c183f9e9df1deeea0906d099a94e8a43047a upstream.

The conditions in irq_exit() to invoke tick_nohz_irq_exit() which subsequently invokes tick_nohz_stop_sched_tick() are:

if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu))

If need_resched() is not set, but a timer softirq is pending then this is an indication that the softirq code punted and delegated the execution to softirqd. need_resched() is not true because the current interrupted task takes precedence over softirqd.

Invoking tick_nohz_irq_exit() in this case can cause an endless loop of timer interrupts because the timer wheel contains an expired timer, but softirqs are not yet executed. So it returns an immediate expiry request, which causes the timer to fire immediately again. Lather, rinse and repeat....

Prevent that by adding a check for a pending timer soft interrupt to the conditions in tick_nohz_stop_sched_tick() which avoid calling get_next_timer_interrupt(). That keeps the tick sched timer on the tick and prevents a repetitive programming of an already expired timer.

Reported-by: Sebastian Siewior bigeasy@linutronix.d Signed-off-by: Thomas Gleixner tglx@linutronix.de Acked-by: Frederic Weisbecker fweisbec@gmail.com Cc: Peter Zijlstra peterz@infradead.org Cc: Paul McKenney paulmck@linux.vnet.ibm.com Cc: Anna-Maria Gleixner anna-maria@linutronix.de Cc: Sebastian Siewior bigeasy@linutronix.de Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1712272156050.2431@nanos Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- kernel/time/tick-sched.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-)

--- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -663,6 +663,11 @@ static void tick_nohz_restart(struct tic tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); }

+static inline bool local_timer_softirq_pending(void) +{ + return local_softirq_pending() & TIMER_SOFTIRQ; +} + static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, ktime_t now, int cpu) { @@ -679,8 +684,18 @@ static ktime_t tick_nohz_stop_sched_tick } while (read_seqretry(&jiffies_lock, seq)); ts->last_jiffies = basejiff;

- if (rcu_needs_cpu(basemono, &next_rcu) || - arch_needs_cpu() || irq_work_needs_cpu()) { + /* + * Keep the periodic tick, when RCU, architecture or irq_work + * requests it. + * Aside of that check whether the local timer softirq is + * pending. If so its a bad idea to call get_next_timer_interrupt() + * because there is an already expired timer, so it will request + * immeditate expiry, which rearms the hardware timer with a + * minimal delta which brings us back to this place + * immediately. Lather, rinse and repeat... + */ + if (rcu_needs_cpu(basemono, &next_rcu) || arch_needs_cpu() || + irq_work_needs_cpu() || local_timer_softirq_pending()) { next_tick = basemono + TICK_NSEC; } else { /*

Patches currently in stable-queue which might be from tglx@linutronix.de are

queue-4.9/nohz-prevent-a-timer-interrupt-storm-in-tick_nohz_stop_sched_tick.patch queue-4.9/timers-invoke-timer_start_debug-where-it-makes-sense.patch queue-4.9/x86-vm86-32-switch-to-flush_tlb_mm_range-in-mark_screen_rdonly.patch queue-4.9/x86-mm-add-the-nopcid-boot-option-to-turn-off-pcid.patch queue-4.9/x86-mm-enable-cr4.pcide-on-supported-systems.patch queue-4.9/sync-objtool-s-copy-of-x86-opcode-map.txt.patch queue-4.9/x86-smpboot-remove-stale-tlb-flush-invocations.patch queue-4.9/timers-use-deferrable-base-independent-of-base-nohz_active.patch queue-4.9/x86-mm-remove-the-up-asm-tlbflush.h-code-always-use-the-formerly-smp-code.patch queue-4.9/x86-mm-reimplement-flush_tlb_page-using-flush_tlb_mm_range.patch queue-4.9/x86-mm-make-flush_tlb_mm_range-more-predictable.patch queue-4.9/x86-mm-remove-flush_tlb-and-flush_tlb_current_task.patch queue-4.9/x86-mm-disable-pcid-on-32-bit-kernels.patch queue-4.9/timers-reinitialize-per-cpu-bases-on-hotplug.patch queue-4.9/x86-mm-64-fix-reboot-interaction-with-cr4.pcide.patch